The present invention generally relates to the manufacture of contact lenses and more specifically relates to methods for cast molding toric contact lenses with a toric optical zone on a surface, for example, on a posterior surface, and preferably a spherical correction on a surface, for example, on an anterior surface.
Contact lenses having a toric optical zone (commonly referred to as xe2x80x9ctoric contact lensesxe2x80x9d) are commonly used to correct refractive abnormalities of the eye relating to astigmatism. Astigmatism may be associated with other refractive abnormalities, such as myopia (nearsightedness), and hypermetropia (farsightedness), presbyopia and the like and therefor toric contact lenses can be prescribed with one or more spherical corrections. Both back toric lenses (having a toric surface formed in the posterior lens surface) and front toric lenses (having a toric surface formed in the anterior lens surface) are presently available.
A toric lens for astigmatism and to correct myopia, hypermetropia, presbyopia and/or one or more other refractive abnormalities will have prescription variables not only for spherical correction but also for toric correction and axis of toric correction. Typically a toric contact lens prescription is available with a toric orientation, (also known as a cylindrical axis) of between 0xc2x0 and 180xc2x0, and usually in increments of no less than 5xc2x0 or 10xc2x0. Whereas spherical contact lenses may freely rotate on the eye, toric contact lenses typically include a ballast, for example, thickened lens section, to inhibit rotation of the lens on the eye such that the cylindrical axis of the toric zone remains generally aligned with the axis of the astigmatism. Thus, the relative orientation of the toric zone or region and the ballast region must be controlled during the contact lens manufacturing process.
A method of manufacturing toric contact lenses is described in Apollonio et al, U.S. Pat. No. 5,611,970, which is incorporated in its entirely herein by reference. In the referenced patent, a toric contact lens is manufactured by using a mold assembly comprising two mold sections. One of the sections defines a contour that corresponds to a ballast section of the lens and another of the mold sections defines a contour corresponding to a toric section of the lens. The two mold sections form a cavity into which a curable mixture of polymerizable monomers is deposited, which will become the material of the molded lens. In accordance with the Apollonio et al patent, the mold sections are placed together and rotated to a specific angle which will define the specific, prescribed xe2x80x9coffsetxe2x80x9d of the toric section in the lens. In order to manufacture a contact lense having a prescribed axis of toric correction, it is conventional that anterior and posterior mold sections are adjustable at multiple rotational positions with respect to one another to align the mold sections at a rotational position corresponding the selected rotational angle. For example, among other variables, the anterior mold half may define the ballast section of the lens and the posterior mold half may define the degree of toric correction.
Thus, during mold assembly, the mold halves are rotated with respect to each other at a desired angle of rotation, to produce a lens having the desired toric orientation.
In conventional cast molding techniques, each mold section is produced by injection molding techniques. A mold insert tool, for example made of metal, ceramic and the like, is provided and secured or fixed in an injection molding machine. A mold section is then produced having the contour of the insert. Thus, the mold section may include a negative impression of, or a contour which corresponds to, a toric zone of a contact lens to be produced from the mold. Similarly, another insert tool is used to produce the opposing mold section, which may include a negative impression of, or a contour corresponding to, a ballast section and preferably the spherical correction, if any, of the contact lense to be produced. The inserts may be used repeatedly in the molding machine in order to produce many identical mold sections or halves.
As disclosed in the above-noted Apollonio et al patent, in order to produce a contact lens, an anterior mold section and a posterior mold section are assembled together after being rotated with respect to each other to the desired degree of offset between the toric area and the ballast section. After polymerization of the monomer or precursor material located in the cavity formed by the assembled mold sections, which polymerization may be initiated by using heat and/or light and/or other energy, the unfinished contact lens product is removed from the mold, while destroying the mold. The contact lens product is finished into a final contact lens using techniques known in the art. One concern with this method is the relative ease with which an error can be made in rotating the mold sections relative to each other. Such an error results in a lens being produced which is not the desired or correct lens. Moreover, if such error occurs, it is likely to be discovered only after the lens product is formed and the mold sections destroyed. Thus, the entire method must be repeated, increasing the cost of producing toric contact lenses.
It would be advantageous to provide a method for producing toric contact lenses which does not rely on relative rotation of the mold halves or sections to properly orient the toric zone and ballast.
New methods for cast molding toric contact lenses and sets of mold sections useful in molding contact lenses have been discovered. The present invention provides ease of manufacturing without the need for complex machinery to align the mold sections prior to assembly or for manufacturing specific tooling for each axis orientation required. The present invention provides mold sections which are easily assembled in the proper rotational orientation. Relative rotation of the mold sections is not required to provide contact lenses having the proper or desired toric zone/ballast orientation.
In a broad aspect of the invention, methods of cast molding a contact lens include the steps of providing a first contact lens mold section, preferably for example, including a negative impression of, or a contour corresponding to, a ballast section or portion of a contact lens; providing a molding apparatus and insert tool to be fixed in the molding apparatus at a plurality of different rotational orientations relative to the molding apparatus; fixing, at one of a plurality of different rotational orientations relative to the molding apparatus, the insert tool in the molding apparatus and producing a second mold section in the molding apparatus with the insert tool fixed thereto. This second mold section includes a negative impression of, or a contour corresponding to, a toric optical zone of a contact lens. The first and second mold sections are assembled.
A polymerizable contact lens material or a contact lens precursor material, for example, a polymer precursor composition conventionally used to produce contact lenses, is provided between the first mold section and the second or toric mold section. The contact lens precursor material, e.g. a monomeric material, is polymerized, for example, by using heat and/or light or other suitable means or energy, between the mold sections to produce a contact lens product. The contact lens product is removed from the first and second mold sections. The first and second mold sections are often destroyed during this removal step. The contact lense product is often an unfinished contact lens which is subjected to one or more finishing steps, for example, conventional finishing steps, to produce the final toric contact lens.
Preferably, the first mold section and the second or toric mold section are adapted to be assembled in only a single rotational orientation, thus substantially eliminating errors in assembling the mold sections. In this embodiment, the assembling step provides the first and second mold sections in a single rotational orientation in which the mold sections can be aligned.
In another broad aspect of the invention, sets of mold sections useful in molding contact lenses. The present sets comprise a first contact lens mold section, preferably including a contour which corresponds to a ballast portion of a contact lens and/or a contour which corresponds to a desired spherical vision correction zone of a contact lens; and a second or toric contact lens mold section including a contour which corresponds to a toric optical zone of a contact lens. The first mold section and the second mold section are adapted to be assembled in only a single rotational orientation. In one very useful embodiment, the set of mold sections comprise a plurality of the first contact lens mold sections, and a plurality of the second contact lens mold sections. In this embodiment, each of the second mold sections is different. In particular, the rotational orientation of the contour which corresponds to a toric optical zone of a contact lens of each second mold section in an assembled first mold section/second mold section combination is different.
Preferably, the first and second mold sections include corresponding forms, such as mating forms, corresponding flats and the like, adapted to at least facilitate assembling and/or locking the first and second mold sections in the single rotational orientation.
The present methods can be employed to produce the present sets for mold sections.
Each and every feature described herein, and each and every combination of two or more of such features, is included within the scope of the present invention provided that the features included in such a combination are not mutually inconsistent.
These and other features, aspects and advantages of the present invention will become apparent hereinafter, particularly when considered in conjunction with the following claims, detailed description and accompanying drawings, in which like parts bear like reference numerals.